allow omitted octets with ipv4

[verfriemelt-dot-org]

heyho,

i really like this service, and a easy way to make it even better would be to support ipv4 ips which omits octets.

$ ping 127.1
PING 127.1 (127.0.0.1) 56(84) bytes of data.

maybe even:

$ ping 127.257
PING 127.257 (127.0.1.1) 56(84) bytes of data.

see https://linux.die.net/man/3/inet_aton and some discussion about that on hackernews: https://news.ycombinator.com/item?id=16728255
the shortest localhost would be 0.nip.io which is also mentioned in the discussion.

$ ping 0
PING 0 (127.0.0.1) 56(84) bytes of data.

thank you for your work :)